Field of the Invention
This invention relates to the field of data storage and management. More particularly, this invention relates to high-performance mass storage systems and methods for data storage, backup, and recovery.
Description of the Related Art
In modern computer systems, collections of data are usually organized and stored as files. A file system allows users to organize, access, and manipulate these files and also performs administrative tasks such as communicating with physical storage components and recovering from failure. The demand for file systems that provide high-speed, reliable, concurrent access to vast amounts of data for large numbers of users has been steadily increasing in recent years. Often such systems use a Redundant Array of Independent Disks (RAID) technology, which distributes the data across multiple disk drives, but provides an interface that appears to users as one, unified disk drive system, identified by a single drive letter. In a RAID system that includes more than one array of disks, each array is often identified by a unique drive letter, and in order to access a given file, a user must correctly identify the drive letter for the disk array on which the file resides. Any transfer of files from one disk array to another and any addition of new disk arrays to the system must be made known to users so that they can continue to correctly access the files.
RAID systems effectively speed up access to data over single-disk systems, and they allow for the regeneration of data lost due to a disk failure. However, they do so by rigidly prescribing the configuration of system hardware and the block size and location of data stored on the disks. Demands for increases in storage capacity that are transparent to the users or for hardware upgrades that lack conformity with existing system hardware cannot be accommodated, especially while the system is in use. In addition, such systems commonly suffer from the problem of data fragmentation, and they lack the flexibility necessary to intelligently optimize use of their storage resources.
RAID systems are designed to provide high-capacity data storage with built-in reliability mechanisms able to automatically reconstruct and restore saved data in the event of a hardware failure or data corruption. In conventional RAID technology, techniques including spanning, mirroring, and duplexing are used to create a data storage device from a plurality of smaller single disk drives with improved reliability and storage capacity over conventional disk systems. RAID systems generally incorporate a degree of redundancy into the storage mechanism to permit saved data to be reconstructed in the event of single (or sometimes double) disk failure within the disk array. Saved data is further stored in a predefined manner that is dependent on a fixed algorithm to distribute the information across the drives of the array. The manner of data distribution and data redundancy within the disk array impacts the performance and usability of the storage system and may result in substantial tradeoffs between performance, reliability, and flexibility.
A number of RAID configurations have been proposed to map data across the disks of the disk array. Some of the more commonly recognized configurations include RAID-1, RAID-2, RAID-3, RAID-4, and RAID-5.
In most RAID systems, data is sequentially stored in data stripes and a parity block is created for each data stripe. The parity block contains information derived from the sequence and composition of the data stored in the associated data stripe. RAID arrays can reconstruct information stored in a particular data stripe using the parity information, however, this configuration imposes the requirement that records span across all drives in the array resulting in a small stripe size relative to the stored record size.
FIG. 21 illustrates the data mapping approach used in many conventional RAID storage device implementations. Although the diagram corresponds most closely to RAID-3 or RAID-4 mapping schemas, other RAID configurations are organized in a similar manner. As previously indicated, each RAID configuration uses a striped disk array 2110 that logically combines two or more disk drives 2115 into a single storage unit. The storage space of each drive 2115 is organized by partitioning the space on the drives into stripes 2120 that are interleaved so that the available storage space is distributed evenly across each drive.
Information or files are stored on the disk array 2110. Typically, the writing of data to the disks occurs in a parallel manner to improve performance. A parity block is constructed by performing a logical operation (exclusive OR) on the corresponding blocks of the data stripe to create a new block of data representative of the result of the logical operation. The result is termed a parity block and is written to a separate area 2130 within the disk array. In the event of data corruption within a particular disk of the array 10, the parity information is used to reconstruct the data using the information stored in the parity block in conjunction with the remaining non-corrupted data blocks.
In the RAID architecture, multiple disks a typically mapped to a single ‘virtual disk’. Consecutive blocks of the virtual disk are mapped by a, strictly defined algorithm to a set of physical disks with no file level awareness. When the RAID system is used to host a conventional file system, it is the file system that maps files to the virtual disk blocks where they may be mapped in a sequential or non-sequential order in a RAID stripe. The RAID stripe may contain data from a single file or data from multiple files if the files are small or the file system is highly fragmented.
The aforementioned RAID architecture suffers from a number of drawbacks that limit its flexibility and scalability for use in reliable storage systems. One problem with existing RAID systems is that the data striping is designed to be used in conjunction with disks of the same size. Each stripe occupies a fixed amount of disk space and the total number of stripes allowed in the RAID system is limited by the capacity of the smallest disk in the array. Any additional space that may be present on drives having a capacity larger than the smallest drive goes unused as the RAID system lacks the ability to use the additional space. This further presents a problem in upgrading the storage capacity of the RAID system, as all of the drives in the array must be replaced with larger capacity drives if additional storage space is desired. Therefore, existing RAID systems are inflexible in terms of their drive composition, increasing the cost and inconvenience to maintain and upgrade the storage system.
A further problem with conventional RAID arrays resides in the rigid organization of data on the disks of the RAID array. As previously described, this organization typically does not use available disk space in an efficient manner. These systems further utilize a single fixed block size to store data which is implemented with the restriction of sequential file storage along each disk stripe. Data storage in this manner is typically inefficient as regions or gaps of disk space may go unused due to the file organization restrictions. Furthermore, the fixed block size of the RAID array is not able to distinguish between large files, which benefit from larger block size, and smaller files, which benefit from smaller block size for more efficient storage and reduced wasted space.
Although conventional RAID configurations are characterized as being fault-tolerant, this capability is typically limited to single disk failures. Should more than one (or two) disk fail or become inoperable within the RAID array before it can be replaced or repaired there is the potential for data loss. This problem again arises from the rigid structure of data storage within the array that utilizes sequential data striping. This problem is further exacerbated by the lack of ability of the RAID system to flexibly redistribute data to other disk areas to compensate for drive faults. Thus, when one drive becomes inoperable within the array, the likelihood of data loss increases significantly until the drive is replaced resulting in increased maintenance and monitoring requirements when using conventional RAID systems.
With respect to conventional data storage systems or other computer networks, conventional load balancing includes a variety of drawbacks. For example, decisions relating to load balancing are typically centralized in one governing process, one or more system administrators, or combinations thereof. Accordingly, such systems have a single point of failure, such as the governing process or the system administrator. Moreover, load balancing occurs only when the centralized process or system administrator can organize performance data, make a decision, and then transmit that decision throughout the data storage system or computer network. This often means that the such load balancing can be slow to react, difficult to optimize for a particular server, and difficult to scale as the available resources expand or contract. In addition, conventional load balancing typically is limited to balancing processing and communications activity between servers only.